For buildings and structures, material selection, energy conservation methods and good water efficiency are important parts to consider when thinking of sustainability. However, thoughts about what could be considered a sustainable foundation are often overlooked (or don’t go much “deeper” than costs or what LEED points it can qualify for). Let's explore how CHANCE helical piles effect the environment, economy, and society to create a more holistic view of what it means to be sustainable.
On land, piling and anchoring solution are abundant and helical anchors have always been known to be cost-effective, versatile, and easy to install. Offshore, however; helical anchors stand alone as the superior choice for mooring applications. First used in the marine environment to secure oil pipelines to the ocean floor, helical anchor technology has been proven to be a successful and environmentally sensitive alternative to traditional mushroom, deadweight, and pile anchors for boat owners, harbormasters, and marine construction and civil engineering firms.
Dry Tortugas National Park is home to historic Fort Jefferson which was constructed for the protection of valuable shipping lanes in the Gulf of Mexico and along the eastern seaboard. The small remote island, only accessible by boat or seaplane, is located 70 miles west of Key West in the Gulf of Mexico and is surrounded by waters, beautiful coral reefs, and protected marine life.
Obstructions can be difficult, because you often do not know they are there until you begin to install a deep foundation. Helical piles cannot install through obstructions; however, here we highlight the different options you have for dealing with obstructions while installing helical piles. One of the benefits of helical piles is that you do not have to abandon the pile. In most cases, it can be removed and reinstalled (unlike other deep foundation options).
Imagine trying to conduct “business as usual” in a building that is being renovated with a new interior second floor addition. That’s exactly what happened on this project.
Helical piles are a displacement piling system that moves the soil away from the central axis of the shaft. This has many advantages that include no spoils to remove, but also comes with disadvantages as the shaft diameter increases. The helical piling industry categorizes pipe helical piles into low, medium, and high displacement. Each category has advantages and disadvantages that a specifying engineer must consider when selecting a pile that is applicable and economical for the project.
The largest volume pipe shaft helical pile used in the North American market are low displacement pipe piles. Low displacement piles are defined as piles with central shaft diameters up to 4.5 inches.
On many construction projects, soil borings are not completed due to the property owner wanting to reduce costs or, quite simply, being unaware of the need to obtain soil strength data for foundation design. During the installation of CHANCE® Helical piles, monitoring torque can provide real time data defining underlying soil strength and its load capacity. As a helical pile is installed (screwed) into increasingly denser/harder soil, the resistance to installation (called installation energy or torque) will increase. The higher the torque, the higher the axial capacity. In most projects, the installation torque increases with depth, and the capacity of CHANCE helical piles can be determined at the time of installation. Regardless of whether the pile is being installed in clay or sand soil, the torque to correlation factor (Kt) for each shaft size, is multiplied by the effective installation torque (T), resulting in the ultimate capacity for each pile. The standard equation for ultimate capacity is Kt * T. The torque correlation factors for CHANCE helical piles can be found in the CHANCE Technical Design Manual-4th Edition. The effective torque is the average torque taken over the last 3 feet of installed depth, measured in 1 foot increments.
The shaft type/size of a helical pile is critical to both the axial and lateral capacity – especially for compression in soft/loose overburden soils where lateral stability of the shaft must be considered. The following is a brief summary of the 4 different shaft types commonly used for helical piles and their relative advantages and disadvantages based on site conditions and application. It is very important to understand that helical pile installation must be considered in the design process.
There are several solutions engineers and contractors can choose from when a deep foundation is required. With a deep foundation the structure’s load is transmitted to soils that are deeper in the ground. A deep foundation is used when a shallow foundation is not possible, not practical, or will not carry the load. Examples are weak, unstable, or expansive surface soils. Two popular options for deep foundations are helical piles and drilled shafts, also known as drilled piers or caissons.